As a daily user of IntelliJ IDEA—which, IME, has the best autocomplete and code suggestions of any IDE for dynamically typed languages—there is a world of a difference between the quality of suggestions for a codebase using TypeScript and one written in vanilla JS. Without concrete types, the IDE often has to guess the possible type(s) that a value can have, whereas with TS, there is (generally) no such ambiguity.
I don't really experience this issue and I use Web storm which is basically the same thing. I find that the dynamic type hinting plus the combination of using JS Doc formatted comments rarely leaves me with any ambiguity when writing vanilla JavaScript.
